1. Field of Invention
The present invention relates to a substrate for an electronic device, a method for manufacturing this substrate for an electronic device, and an electronic device.
2. Description of the Related Art
In the related art, ferroelectric memories which are nonvolatile memories using ferroelectrics has been used.
These ferroelectric memories are classified into a capacitor type, in which a 1T/1C structure, etc., is formed using ferroelectrics as capacitors, and an MFSFET type, in which ferroelectrics are used as gate insulating films of field-effect transistors in place of SiO2.
The MFSFET type ferroelectric memory has advantages over the capacitor type, for example, it increases the packing density and non-destructive read-out. However, the MFSFET type is difficult to manufacture with respect to the structure. Thus, under present circumstances, development and commercialization of the capacitor type ferroelectric memory have been more advantageous.
Ferroelectric materials adopted in the capacitor type ferroelectric memories are divided into two materials, Pb(Zr1-xTix)O3 (PZT) and SrBi2Ta2O9 (SBT). Among them, the PZT materials having compositions in the neighborhood of the rhombohedron-tetragonal phase boundary (MPB) are superior in the residual dielectric polarization and coercive electric field property, and are the materials which are more advantageous than the others in commercialization.
In the related art, Pt has been used as a PZT-based ferroelectric material for a lower electrode. Since Pt has a face-centered cubic lattice structure that is a close-packed structure, it has a strong self-orientation property, and therefore brings about cubic crystal orientation even on amorphous, such as SiO2.
However, since the orientation property is strong, there have been problems in that when a columnar crystal of Pt has grown, Pb, for example, is likely to diffuse in a substrate along grain boundaries, adhesion between Pt and SiO2 is degraded, and the like.
Although Ti may be used to enhance this adhesion between Pt and SiO2, and furthermore, TiN, etc., may be used as diffusion barrier layers against Pb, etc., electrode structures become complicated, and in addition, oxidation of Ti, diffusion of Ti into Pt, and reduction in crystallinity of PZT accompanying that are brought about, and therefore degradation of the polarization electric field (P-E) hysteresis characteristic, the leakage current characteristic, and the fatigue characteristic occur.
In order to address or avoid problems of Pt electrodes as described above, RuOx, IrO2, and other conductive oxide electrode materials have been researched. Among them, in particular, SrRuO3 having a perovskite structure has the same crystal structure as that of PZT, and therefore has superior joining property at the interface, is likely to realize epitaxial growth of PZT, and has superior characteristics as a diffusion barrier layer against Pb.
Consequently, the related art has researched ferroelectric capacitors using SrRuO3 as an electrode.